1,721,165 research outputs found
Chemo-physical evolution and microstructure features of lime treated soils
No full textIn the paper some results on the effects of chemo-physical evolution of clay-lime-water suspensions on the microstructure of a lime treated kaolin have been presented. A multi-scale investigation on the sedimentation behaviour of clay suspensions under different pore water chemistry has been developed highlighting the chemo-physical mechanisms controlling particle arrangement and the soil fabric formation. The results evidenced the key role of ionic exchange in the short term on the microstructure features of the lime treated soil
Study of the mechanisms of drug passage through biological barriers aimed to optimize bioavailability and/or blood-brain barrier permeation
No full textPhospholipophilicity, i.e. the affinity of a drug for phospholipids, is one of the key features modulating pharmacokinetics. It would be desirable to assess it in the early stages of pharmaceutical drug development. The fastest method to achieve phospholipophilicity measures is liquid chromatography performed on stationary phases functionalized with phospholipid analogues, so called Immobilized Artificial Membrane (IAM). The logarithms of the chromatographic retention coefficients of drugs, measured or extrapolated to 100% aqueous phase on such stationary phases (log kwIAM), are often used to surrogate drug membrane passage data measured in vivo or in situ. Indeed, the research group I worked with proposed a novel method to unravel the total drug/phospholipid interaction forces in a lipophilic/hydrophobic component, mainly described by the n-octanol/water lipophilicity, possibly acting as a “driving force” in membrane barrier passage, and a polar/electrostatic one, possibly acting instead as a “trapping force”. The latter is parameterized by ∆log kwIAM, a novel physico-chemical parameter proposed by the research team I worked with. It is the difference between phospholipophilicity values determined by IAM-HPLC (log kwIAM) and the values expected on the basis of n-octanol/water lipophilicity of the neutral forms of the analytes (log PN). The rationale of this parameter arises from the fact that log kwIAM values of structurally non-related neutral compounds having polar surface area (PSA) equal to zero relate unambiguously with n-octanol lipophilicity values by highly significant direct linear relationships (r2 0.96) in a log P range 1.15-4.80; in contrast, such relationships are no longer observed for analytes having PSA greater than 0 and, in larger extent, for ionizable analytes. In fact, for instance, poorly and medially lipophilic bases, ionized at the experimental conditions, show an IAM chromatographic retention higher than that of neutral isolipophilic compounds. Such peculiar behavior was referred to the occurrence of an extra interaction component, mainly of electrostatic nature, actually taking place in drug-phospholipid interaction. ∆log kwIAM was found as a suitable descriptor of the drug/biomembrane polar/electrostatic interaction component. This component was demonstrated as related by highly significant inverse linear relationships to Blood-Brain Barrier (BBB) penetration data (log BB). For the BBB passage of acidic compounds, it was necessary to magnify the electrostatic interaction component by calculating it taking into account log D7.4 rather than log PN so yielding ∆’log kwIAM values. In this Ph.D. thesis, a study has been performed for (a) the elucidation of the molecular mechanisms actually involved in drug/biomembrane interactions (b) verifying the soundness of ∆log kwIAM in predicting different data of passive drug uptake either measured in vivo or in vitro (c) the improvement of the throughput of the technique so as to offer to the pharmaceutical companies an high-throughput screening method to evaluate new drug candidates. The relationships between data of BBB penetration (log BB) and ∆log kwIAM reported in recent works were based on a limited dataset (n= 21). As a consequence, the first part of the present research was focused on validating the proposed model on an enlarged dataset. Therefore, further 21 analytes, whose log BB values were known and taken from a single bibliographic source, were taken into account and their chromatographic retention coefficients were determined on two different stationary phases, i.e. IAM.PC.MG and IAM.PC.DD2. A good relationship between log BB and log PN values could be observed after the exclusion of two data points (chlorambucil and domperidone), but fairly good and highly significant inverse linear relationships were observed between log BB and ∆log kwIAM.MG (r2 = 0.681) and ∆log kwIAM.DD2 (r2 = 0.825), respectively, for the all the analytes. The results from our previous work were then assembled with the newly determined values in a single doubled dataset (n = 42) to verify the model proposed; again remarkably significant linear inverse relationships were achieved when plotting log BB values vs either ∆log kwIAM.MG (r2 = 0.738) or ∆log kwIAM.DD2 (r2 = 0.826), with only two points (haloperidol and chlorpromazine) behaving as outliers. Subsequently, starting from the observation according to which membrane passive diffusion of analytes has been suggested to be a universal process, regardless the different composition or function of the biological barrier involved, possible relationships between delta values and intestinal absorption data as measured by the in situ LOC-I-GUT perfusion technique were for the first time investigated. For this second part of this research activity, 15 structurally unrelated analytes, known to be passively absorbed at intestinal level, were taken into account and their IAM chromatographic retention coefficients were determined. Although moderate linear direct relationships between intestinal absorption data and log P values were found, again much more significant relationships were obtained by plotting intestinal absorption data vs ∆log kwIAM.MG (r2 = 0.803) and ∆log kwIAM.DD2 (r2 = 0.784). However, these results, albeit really encouraging, were based on a limited dataset. However, this model had to be validated by taking into account a larger number of biological data, and this opportunity was provided by permeation data achieved on cultured cells model, such as Caco-2 and MDCK cultured cells. Indeed, Caco-2 and MDCK permeation assays, for the morphological similarity of cellular monolayers employed to the intestinal epithelium, are claimed as mirroring rather closely drug intestinal absorption. However, in such assays the in vitro apparent permeability values, log Papp, i.e. the crude permeation data, can be separated into four contributions i) aqueous boundary layer (represented by the accessible intestinal surface area - PABL), ii) filter-determined permeability related to the polycarbonate porous support of the cultured cells (Pf), transcellular permeability (PC), and paracellular permeability (Ppara). The role played by these contributions markedly differs between in vitro and in vivo systems. Therefore, the investigation was carried out employing two datasets: the first one consisting of 38 compounds whose crude Caco-2 permeation data, log Papp, were reported in the literature; the second one consisting of 47 compounds whose Caco-2/MDCK permeation data were corrected to express the sole transcellular intrinsic permeability of the drugs, log P0Caco-2/MDCK. As to the the first dataset, log Papp values were found as related to the apparent lipophilicity of the analytes measured at pH 7.4 (log D7.4) by a parabolic trend, and reasonable relationships between log Papp and delta values were only visible selecting the analytes heavier than 300 Da. Indeed, for these compounds, the occurrence of paracellular passage mechanisms can be reasonably excluded. On the other hand, when taking into account the second dataset, highly significant inverse linear relationships between log P0Caco-2/MDCK and ∆log kwIAM.MG (r2 = 0.765) and ∆log kwIAM.DD2 (r2 = 0.806) were achieved. Indeed, log P0Caco-2/MDCK express the sole transcellular intrinsic permeability. The last part of this Ph.D. project was devoted to the improvement of throughput technique so as to appeal pharmaceutical companies, too. The first strategy applied was the development and validation of partial-least-squares (PLS) based statistic models, starting from molecular descriptors calculated in silico aimed at predicting phospholipophilicity data measured on IAM stationary phases. This led to the development of two mathematical models able to predict phospholipophilicity as measured on IAM.PC.MG and IAM.PC.DD2, with an accuracy of 75% and 79%, respectively. These results allow a rapid and reliable in silico prediction of delta log kwIAM values suitable for accurate estimates of the intestinal absorption/BBB entering potential of new leads or hypothetical molecules. In parallel, the conditions of the analytical methods were optimized to gain experimental values in a reasonably short time. The coupling of the LC system to an Electrospray Ionization Source (ESI) – Time of Flight (TOF) mass spectrometer detector allowed to analyze the compounds of interest simultaneously in mixtures of up to 10 compounds at the same time thanks to the higher selectivity of m/z ratio. This approach resulted in the development of an MS analytical method 100 times faster than the one traditionally employed in this sort of determinations
Naturalization record of Russo, Giacomo
No full textThe naturalization certificate for Giacomo Russo of Italy. Signed by Judge Joseph B. Wall
Relationships between human intestinal absorption and polar interactions drug/phospholipids estimated by IAM-HPLC
No full textPhospholipid affinity indexes (logkW(IAM)) for 15 structurally non-related basic, acidic, ampholytic, and neutral drugs were measured by HPLC on two different phospholipid stationary phases (immobilized artificial membrane - IAM). According to a method we previously proposed, polar and electrostatic forces involved in drug/membrane interactions were quantified both as ΔlogkW(IAM) and as Δ(')logkW(IAM). These values are the differences between the experimental logkW(IAM) and the values expected for a neutral compound having the lipophilicity value equal to either that of the neutral form of the analyte (logP(N)) or that of the mixture of charged and neutral forms of the analyte at jejunum pH 6.5 (logD(6.5)), respectively. Jejunum absorption values, logPeff, measured by the Loc-I-Gut technique, did not relate with logkW(IAM) values. A moderate linear relationship was observed with logP(N) values for all the analytes and a weak parabolic relationship was observed with logD(6.5) values, but only after the exclusion of two analytes. In contrast, a highly significant linear inverse relationship was observed with ΔlogkW(IAM) values. Therefore, differently from the results of our recent studies on blood-brain barrier passage, the intestinal absorption data for not only bases and zwitterions but also for acids relate significantly with ΔlogkW(IAM) and not with Δ(')logkW(IAM) values. The results suggest that membrane passage at jejunum level can be described according to the "flip-flop" model; indeed, the lipophilicity of the neutral forms (logP(N)) appears related to the passage through the non-polar inner moieties of phospholipids whereas ΔlogkW(IAM) parameter appears related to the "trapping" forces at their polar surfaces. The method, easy to perform and at medium throughput, could be of use for preliminary screening of new drugs based on oral absorption potential
Immobilized Artificial Membrane HPLC Derived Parameters vs PAMPA-BBB Data in Estimating in Situ Measured Blood-Brain Barrier Permeation of Drugs
No full textThe affinity indexes for phospholipids (log kWIAM) for 42 compounds were measured by High Performance Liquid Chromatography (HPLC) on two different phospholipid-based stationary phases (Immobilized Artificial Membrane - IAM). The polar/electrostatic interaction forces between analytes and membrane phospholipids (Δlog kWIAM) were calculated as the differences between the experimental values of log kWIAM and those expected for isolipophilic neutral compounds having Polar Surface Area (PSA) = 0.
The values of Blood-Brain barrier (BBB) passage measured in situ, P0in situ, for 38 analytes were taken from the literature, representing the permeability of the neutral forms on “efflux minimized” rodent models. Furthermore, the values of passage through a porcine brain lipid extract (PBLE) artificial membrane for 36 analytes, measured by so-called PAMPA-BBB technique, were taken into account (P0PAMPA-BBB). A total of 42 compounds were considered, being 32 analytes in common to both sets.
The values of log P0PAMPA-BBB were found significantly related to the n-octanol lipophilicity of the neutral forms (log PN) whereas poor relationships were found with lipophilicity of the mixtures of ionized and neutral forms existing at the experimental pH 7.4 (log D7.4). Furthermore no relationship was found with either log kWIAM or Δlog kWIAM values. The values of log P0in situ related moderately to log P0PAMPA-BBB (32 data points) but did not relate with either n-octanol lipophilicity indexes (log PN and log D7.4) or phospholipid affinity indexes (log kWIAM). In contrast, significant inverse linear relationships were observed between log P0in situ (38 data points) and Δlog kWIAM values for all compounds but ibuprofen and chlorpromazine who behaved as moderate outliers. It should be remembered that BBB passage, parameterized by log BB values, i.e. the logarithm of the ratio brain concentration/ blood concentration, was previously found linearly related to Δlog kWIAM for bases, ampholytes, and neutral compounds whereas for acids the measure of polar/electrostatic interactions required the correction for ionization giving a different parameter, Δ’log kWIAM. However, the result of the present work are not in contrast with the results previously found because log P0in situ refer to the “intrinsic permeability” of the analytes regardless their ionization degree. Furthermore, log BB values and log P0in situ are roughly linearly related for all the analytes but those predominantly present at the experimental pH 7.4 as anions. The latter are included in the relationship only if log P0in situ values corrected for ionization (log PCin situ) are taken into account.
These results suggest that ΔlogkWIAM parameter is effective at predicting log P0in situ values for all the analytes and that ionization affects much more markedly BBB passage of acids (yielding anions) than that of the other ionisable compounds
Indexes of polar interactions between ionizable drugs and membrane phospholipids measured by IAM-HPLC: their relationships with data of blood-brain barrier passage.
No full textPhospholipid affinity indexes (logkWIAM) for 21 structurally non-related basic, acidic, ampholytic, and neutral drugs were measured by HPLC on two different phospholipid stationary phases (Immobilized Artificial Membrane - IAM). The differences between the experimental values and those expected for neutral isolipophilic compounds (??/??'logkwIAM) were assumed as a measure of polar and electrostatic forces involved in the interactions drug/membrane. Blood Brain Barrier (BBB) permeation data (log BB) weakly related with n-octanol lipophilicity values of the neutral forms (log PN), but only after the exclusion of two analytes. No relationship was observed with the lipophilicity of the mixture of charged and neutral forms (log D7.4) and very poor relationships were also found with values. In contrast, a good linear inverse relationship was found between log BB and ??/??'logkwIAM values. This relationship was also observed on an enlarged set of 42 data points obtained by assembling the drugs considered with 21 drugs examined in our previous works (acids and bases).
The results suggest that ??/??' logkwIAM parameter, as a sole descriptor, is effective in evaluating the capability of a compound to cross the BBB, indicating that the polar/electrostatic interactions, which are the additional interactions described by IAM, are of prime importance in predicting BBB passage
Development and Validation of a LC-FD Method for the Simultaneous Determination of Eight Bisphenols in Soft Drinks
No full textBisphenol A (BPA) is a chemical widely used as a monomer in the production of polymers of plastics. It acts as an endocrine disrupting agent and thus its contaminations of food and beverage should be carefully monitored in order to assess consumers’ risk. In this study we propose a liquid chromatography-fluorescence detection (LC-FD) validated method for the simultaneous determination of BPA and seven analogues, i.e. bisphenol AF, bisphenol B, bisphenol E, bisphenol F, BPA diglycidyl ether, bisphenol F diglycidyl ether, and Bisphenol M in soft drinks. A one-step solid phase extraction (SPE) was effective at reducing the interferences, obtaining good purification of the samples and, consequently good recoveries of all analytes. The separation was obtained on a C18 column by using acetonitrile/water 55:45 (v/v) under isocratic conditions. Method validation was performed according to the European Commission Decision 2002/657/EC criteria, providing good results regarding the analytical parameters of linearity, selectivity, sensitivity, precision, recovery, decision limit (CCα), detection capability (CCβ), limit of detection (LOD), limit of quantification (LOQ), stability and robustness. The method allows the detection of BPA and BADGE at levels much lower than their legal limits in the food, which are 0.06 mg kg-1 and 9.00 mg kg-1, respectively
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